Invariant-based reasoning about parameterized security protocols

We explore the applicability of the programming method of Feijen and van Gasteren to the domain of security protocols. This method addresses the derivation of concurrent programs from a formal specification, and it is based on common notions like invariants and pre- and post-conditions. We show that fundamental security concepts like secrecy and authentication can nicely be specified in this way. Using some small extensions, the style of formal reasoning from this method can be applied to the security domain. To demonstrate our approach, we discuss an authentication protocol and a public-key distribution protocol, and we deal with their composition. By focussing on a general setting where agents run the protocols multiple times, the nonce concept turns out to pop-up naturally. Although this work does not contain any new protocols, it does offer a new view on reasoning about security protocols.     

Nature of the second optical transition in PbSe nanocrystals

The second peak in the optical absorption spectrum of PbSe nanocrystals is arguably the most discussed optical transition in semiconductor nanocrystals. Ten years of scientific debate have produced many theoretical and experimental claims for the assignment of this feature as the 1P e1P h as well as the 1S h,e1P e,h transitions. We studied the nature of this absorption feature by pump-probe spectroscopy, exactly controlling the occupation of the states involved, and present conclusive evidence that the optical transition involves neither 1S e nor 1S h states. This suggests that it is the 1P h1P e transition that gives rise to the second peak in the absorption spectrum of PbSe nanocrystals.     

Dutch and American waterway development: identification and classification of instruments for value creation

Waterways can serve society in a variety of ways. However, authorities responsible for maintenance and development of waterways often have a sectoral focus. They strive for cost-efficient solutions within their restricted scope; broader development of socio-economic value receives little attention. This can be seen in, e.g. the Netherlands and the USA. Both countries have strong national authorities responsible for the navigation function of waterways. The societal call for broader optimization is recognized, but a systemized response to this call is lacking. Nevertheless, both authorities make attempts towards increasing the socio-economic value of their capital waterway projects by deploying instruments for broader optimization. Six recent cases, in which such attempts were made, are studied with the aim of identifying and classifying the instruments deployed. Identification and classification are needed to evaluate where gaps and opportunities lie for more systemized responses. From these cases, a total of 15 instruments are identified which stimulated broad optimization. These instruments are classified by identifying the transaction characteristics associated with these instruments. The results show overlaps and voids in the domains these instruments address. For practitioners, the results can be helpful to navigate through the planning and implementation phase of waterway projects.     

Regioselective Organocatalytic Formation of Carbamates from Substituted Cyclic Carbonates

A highly regioselective catalytic approach has been developed towards carbamates derived from cyclic organic carbonates by reaction of the latter with amine reagents under organocatalytic control. For various combinations of carbonate and amine substrates, an organocatalyst (TBD: 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene) was used to increase the reaction kinetics while exerting excellent regioselective control. The current method is the first general approach towards the control over the regioselectivity of this reaction using a wide variety of easily accessed substituted organic carbonates.

     

Molecular characterization of lactic acid bacteria and in situ amylase expression during traditional fermentation of cereal foods

Lactic acid bacteria play an important role in traditional fermented foods consumed in different countries. Study of their taxonomic structure and diversity is necessary for starter culture selection, improved safety and nutritional enhancement. To achieve these objectives, microbial genomic typing methods were used to study genetic differences of autochthonous bacteria and their distribution in two traditional African fermented cereal foods. A total of 85 predominant bacterial species were isolated from ogi and kunu-zaki obtained from Northern and Southern geographical region of Nigeria. They were identified using combination of 16S rRNA gene sequencing, multilocus sequence analysis (MLSA) based on rpoA, pheS and atpA genes as well as M13-PCR gel fingerprints. The results showed that Lactobacillus fermentum was the most frequently isolated species in ogi (71.4%) and kunu-zaki (84.5%). Other species of lactic acid bacteria (LAB) identified were Lactobacillus plantarum, Streptococcus gallolyticus subsp. macedonicus and Pediococcus pentosaceus. Non lactic acid bacteria isolated from these foods were species belonging to the Bacillus and Staphylococcus. Non-metric multidimensional scaling (nMDS) analysis of the M13-PCR fingerprints for LAB strains showed clonal diversity among strains of the same species. In vitro and in situ expression of amylase gene during fermentation by amylolytic L. plantarum ULAG11 was detected, indicating the potential usefulness of such species for development of starter cultures and for controlled fermentation processes.     

A Model of Foam Filters

Filtration with foam filters is reported as a successful method to remove inclusions from top-cut silicon scrap. Inclusions in top-cut silicon scrap are needle-like Si₃N₄ particles and round SiC inclusions. A high filtration efficiency of more than 99 pct for 30-ppi SiC filters is achieved. The inclusions that remain are mainly SiC particles smaller than 10 μm. Possibly these particles are primarily secondary inclusions. The filtration efficiency increases with decreasing filter pore size. The main factor that plays a role in deep-bed filtration seems to be interception. Various models are considered to estimate the removal efficiency of foam filters by this mechanism. Here, we propose a new model called “the branch” model. This model gives a high filtration efficiency and agrees the best with the experimental results.     

Oil is a sedimentary supersorbent for polychlorinated biphenyls

The often-observed enhanced sorption of hydrophobic organic chemicals (HOCs) to sediments is frequently attributed to the presence of soot and soot-like materials. However, sediments may contain other hydrophobic phases, such as weathered oil residues. Previous experiments have shown that these residues can be efficient sorbents for certain PAHs. In this study we investigated sorption of PCBs to sediments contaminated with different concentrations and types of oils, and from that derived oil-water distribution coefficients (Koil). Sorption of PCBs to both fresh and weathered oils was proportional to sorbate hydrophobicity, and no effects of PCB planarity were observed. Furthermore, the experiments demonstrated that different oils sorbed PCBs similarly and extensively (Koil up to 108.3 for PCB 169), and that weathering caused an almost 2-fold increase in sorption of the lower chlorinated PCBs. Koil values indicated that at the PCB equilibrium concentrations tested (pg-ng/L range), for many congeners weathered oil is a stronger sorbent than pure soot and soot-like materials. Due to attenuation of adsorption to the latter materials in sediments (caused by competitive adsorption with organic matter), sedimentary weathered oil will therefore, if present as a separate phase, defeat sedimentary soot, coal, and charcoal as PCB sorbent in most cases. Consequently, weathered oil probably is the ultimate sedimentary sorbent for PCBs and should be included in HOC fate models.     

Alternative 2D Shape Representations using the Symmetry Set

Among the many attempts made to represent families of 2D shapes in a simpler way, the Medial Axis takes a prominent place. Its graphical representation is intuitively appealing and can be computed efficiently. Small perturbations of the shape can have large impact on the and are regarded as instabilities, although these changes are mathematically known from the investigations on a super set, the Symmetry Set . This set has mainly been in a mathematical research stage, partially due to computational aspects, and partially due to its unattractive representation in the plane. In this paper novel methods are introduced to overcome both aspects. As a result, it is possible to represent the as a string is presented. The advantage of such a structure is that it allows fast and simple query algorithms for comparisons. Second, alternative ways to visualize the are presented. They use the distances from the shape to the set as extra dimension as well as the so-called pre-Symmetry Set and anti-Symmetry Set. Information revealed by these representations can be used to calculate the linear string representation structure. Example shapes from a data base are shown and their data structures derived. Arjan Kuijper is Senior Researcher at the Johann Radon Institute (RICAM) of the Austrian Academy of Sciences in Linz, Austria. He received his M.Sc. degree in applied mathematics in 1995 from the University of Twente, The Netherlands. During the period 1996–1997 he worked at ELTRA Parkeergroep, Ede, The Netherlands. He has been a Ph.D. student (1997–2001), associate researcher (2001–2002), and postdoc (202) at the Institute of Information and Computing Sciences of Utrecht University. In 2003-2005 he served as assistant research professor at the IT University of Copenhagen in Denmark. His interest subtends all mathematical aspects of image and shape analysis, notably multi-scale representations (scale spaces), catastrophe and singularity theory, medial axes and symmetry sets, partial differential equations, singular theories, and their applications. Ole Fogh Olsen is associate professor in the image group at the IT University of Copenhagen. He received the PhD degree in 2000 in computer science from University of Copenhagen, Denmark. Main research interest areas are image analysis, medical image analysis and computer vision with focus on scale space theory, differential geometry, singularity theory, statistics, segmentation, optic flow and shape modelling. Peter Giblin is Professor of Mathematics at the University of Liverpool and a former Head of the Mathematical Sciences Department. He joined the staff there in 1967 and has been visiting professor at the University of North Carolina at Chapel Hill, Five Colleges in Amherst, Massachusetts, and Brown University. His research interests are in singularity theory and its applications to differential geometry and computer vision. Mads Nielsen received a MSc in 1992 and a PhD in 1995 both in computer science from DIKU, Department of Computer Science, University of Copenhagen, Denmark. During his PhD studies he spent one year 93–94 at the Robotvis lab at INRIA, Sophia-Antipolis, France. In the second half of 1995 he was post-doc at the Image Sciences Institute of Utrecht University, The Netherlands. In 1996 he was joint post-doc at DIKU and 3D-Lab, School of Dentistry, University of Copenhagen, where he served as assistant professor 1997–99. In 1998–99 he served as external associate professor at Institute of Mathematical Modelling, Technical University of Denmark. April 1999 he became the first associate professor at the new IT University of Copenhagen. Since June 2002 he has been professor the same place heading the Image Analysis Group. He is head of the PhD-studies at ITU, member of the Academical Council of ITU, General chair of MICCAI 2006, member of the editorial board of IJCV and JMIV. His research interests are in the mathematical foundation of image analysis, the computational aspects, and the applications, especially in the medical area.